EP0878028A1 - Process for the production of an electrode for a fused carbonate fuel cell, electrode produced according to this process and fused carbonate fuel cell provided with an electrode produced according to this process - Google Patents

Process for the production of an electrode for a fused carbonate fuel cell, electrode produced according to this process and fused carbonate fuel cell provided with an electrode produced according to this process

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Publication number
EP0878028A1
EP0878028A1 EP97904358A EP97904358A EP0878028A1 EP 0878028 A1 EP0878028 A1 EP 0878028A1 EP 97904358 A EP97904358 A EP 97904358A EP 97904358 A EP97904358 A EP 97904358A EP 0878028 A1 EP0878028 A1 EP 0878028A1
Authority
EP
European Patent Office
Prior art keywords
electrode
plates
fuel cell
lithium
lithium cobaltite
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP97904358A
Other languages
German (de)
French (fr)
Other versions
EP0878028B1 (en
Inventor
Manfred Bischoff
Bernd Rohland
Uwe Jantsch
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MTU CFC Solutions GmbH
Rolls Royce Solutions GmbH
Original Assignee
MTU Friedrichshafen GmbH
MTU Motoren und Turbinen Union Friedrichshafen GmbH
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Publication of EP0878028A1 publication Critical patent/EP0878028A1/en
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Publication of EP0878028B1 publication Critical patent/EP0878028B1/en
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H01M4/8857—Casting, e.g. tape casting, vacuum slip casting
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8875—Methods for shaping the electrode into free-standing bodies, like sheets, films or grids, e.g. moulding, hot-pressing, casting without support, extrusion without support
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
    • H01M4/8882—Heat treatment, e.g. drying, baking
    • H01M4/8885—Sintering or firing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/14—Fuel cells with fused electrolytes
    • H01M8/141—Fuel cells with fused electrolytes the anode and the cathode being gas-permeable electrodes or electrode layers
    • H01M8/142—Fuel cells with fused electrolytes the anode and the cathode being gas-permeable electrodes or electrode layers with matrix-supported or semi-solid matrix-reinforced electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
    • H01M2004/8689—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/14—Fuel cells with fused electrolytes
    • H01M2008/147—Fuel cells with molten carbonates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0048—Molten electrolytes used at high temperature
    • H01M2300/0051—Carbonates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the invention relates to a method for producing an electrode for a molten carbonate fuel cell, to an electrode produced by the method and to a molten carbonate fuel cell with an electrode produced by the method.
  • lithium cobaltite LiCo O 2
  • LiCo O 2 lithium cobaltite
  • a dispersant can be added to the binder.
  • a film is formed from the mixture, which is divided into plates. The plates are sintered in an air-carbon dioxide atmosphere at high temperatures.
  • Lithium cobaltite is produced by reacting cobalt with lithium compounds (EP 0 473 236 A2).
  • lithium cobaltite as a powder by reacting cobalt oxide (iron oxide) with lithium hydroxide vapor in a high-temperature reaction.
  • This powder is processed by means of ceramic sintering processes into small-size, fragile electrode plates (JP 0636, 770).
  • lithium cobaltite layer by oxidation from a ductile cobalt layer whose pores are filled with lithium carbonate.
  • the conversion to the lithium cobaltite layer preferably takes place after combination with a matrix layer and an anode layer and after insertion together with current collectors in a cell holder of a fuel cell during a start-up phase of the fuel cell.
  • the structure of the lithium cobaltite electrode plate thus produced corresponds to the structure of the original porous cobalt electrode plate, which has a relatively large polarization resistance (DE 43 03 136 Cl).
  • the invention is based on the problem of a method for producing a porous lithium cobaltite electrode plate with a large inner surface and a small one Specify polarization resistance and provide an electrode plate produced by the method.
  • the problem is solved for the process according to the invention in that cobalt metal and lithium carbonate powders are homogeneously mixed with one another, in that the mixture is then used to produce foils and sheets from the foils, which are sintered to form porous electrode precursor plates, and that the electrode precursor plates are then at a temperature between 400 ° C and 488 ° C flowing air for several hours until the electrode precursor plates are converted into lithium cobaltite electrode plates with an extremely large inner surface.
  • a structure-determining formation reaction of lithium cobaltite takes place in several stages. First of all, cobalt / lithium carbonate precursor electrode plate oxidizes cobalt in the air atmosphere.
  • lithium cobaltite and lithium oxide are formed with the emission of carbon dioxide, which is removed with the flowing air. Because of its high vapor pressure, lithium oxide changes into the gas phase, in which it reacts to cobalt oxide not contacted with lithium carbonate to form lithium cobaltite.
  • the temperature is maintained between 420 ° C and 480 ° C during the formation of lithium cobaltite. It has been shown that in this temperature range the reactions described above take place under the action of atmospheric oxygen under favorable conditions.
  • the amount of air supplied and the flow rate of the air are adjusted so that the carbon dioxide content of the air is not more than about 1% and the duration of exposure to the air is about 10 hours.
  • the forming process to form a large inner surface> 2 m 2 / g can also be carried out with CO 2 contents> 1% in the forming gas atmosphere.
  • LiCoO 2 is formed by the reaction of oxidized cobalt and lithium hydroxide according to the following mechanism.
  • the method according to the invention can be carried out after inserting the electrode precursor plates into an oven under the conditions described above, the lithium cobaltite electrodes produced being removed from the oven after cooling and then with a matrix layer impregnated with the melt electrolyte and an anode and with current collectors be put together in a fuel cell.
  • the respective electrode precursor plate is combined with a matrix layer filled with molten carbonate to form a layer arrangement corresponding to the fuel cell and is then installed with the latter in a fuel cell, the method according to the invention being carried out after installation in the fuel cell.
  • the lithium cobaltite cathode is formed during a startup procedure of the fuel cell.
  • the lithium cobaltite can also be produced as a thin, firmly adhering layer on a porous base made of nickel, which is thereby oxidized.
  • the starting components are fine cobalt powder with a grain size of ⁇ 3 ⁇ m and Li 2 CO 3 powder, which has a grain size between l ⁇ m and lO ⁇ m, in a ratio of 66% by weight Co and 34% by weight Li 2 CO 3 with the addition of a processed in a non-aqueous solvent organic binder, a plasticizer, and other organic additives to form a viscous slip, which is pulled out into a film using the "tape casting" process.
  • sheets are produced from the film, which are sintered in a protective gas furnace at a temperature below the Li 2 CO 3 melting point, preferably at 650 ° C., for 30 minutes in a reducing atmosphere.
  • the plates After this procedure there is a close one Contact between the Co and the Li 2 CO 3 grains in the electrode precursor plates.
  • the plates After the plates have been sintered, they are cooled to 460 ° C. at a rate of 200 Kelvin per hour and, after adequate purging with nitrogen, they are changed to an air atmosphere with an air exchange. At this temperature, the complete oxidation of Co takes place within 10 hours with simultaneous formation of lithium cobaltite from the cobalt oxide formed and Li 2 CO 3 in a solid-state and gas reaction.
  • the lithium cobaltite electrode thus produced has an extremely large inner surface, which is retained after installation in a molten carbonate fuel cell and its operation.
  • the forming speed is determined by (i) the content of carbon dioxide and water vapor and (ii) the grain size of the cobalt and the Li 2 CO 3 powder.
  • An electrode produced by the method according to the invention has a structure typical of the method with an extremely large inner surface. This results in a very low polarization resistance of a corresponding cathode in a fuel cell, which increases its performance.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Materials Engineering (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Inert Electrodes (AREA)

Abstract

The invention concerns a process for the production of a porous lithium cobaltite electrode plate with a large inner surface and low polarization resistance. Lithium carbonate powder and cobalt metal powder are uniformly mixed together and then films are produced from the mixture and plates from the films, which plates are sintered and then placed in an air stream for several hours at a temperature between 400 °C and 488°C until the conversion of said plates to lithium cobaltite electrode plates with an extremely large inner surface has taken place.

Description

B E S C H R E I B U N G DESCRIPTION
Verfahren zur Herstellung einer Elektrode für eine Schmelzkarbonat-Brennstoffzelle, nach dem Verfahren hergestellte Elektrode und Schmelzkarbonat-Brennstoffzelle mit einer nach dem Verfahren hergestellten ElektrodeMethod for producing an electrode for a molten carbonate fuel cell, electrode produced by the method and molten carbonate fuel cell with an electrode produced by the method
Die Erfindung bezieht sich auf ein Verfahren zur Herstellung einer Elektrode für eine Schmelzkarbonat-Brennstoffzelle, auf eine nach dem Verfahren hergestellte Elektrode und auf eine Schmelzkarbonat-Brennstoffzelle mit einer nach dem Verfahren hergestellten Elektrode.The invention relates to a method for producing an electrode for a molten carbonate fuel cell, to an electrode produced by the method and to a molten carbonate fuel cell with an electrode produced by the method.
Es ist bekannt, Kathoden für Schmelzkarbonat-Brennstoffzellen aus Lithiumcobaltit (LiCo O2) zu erzeugen. Zur Herstellung derartiger Kathoden wird Lithiumcobaltit-Pulver mit einem Bindemittel vermischt. Ein Dispergiermittel kann dem Bindemittel beigemischt werden. Aus der Mischung wird eine Folie gebildet, die in Platten geteilt wird. Die Platten werden in einer Luft-Kohlendioxid-Atmosphäre bei hohen Temperaturen gesintert. Lithiumcobaltit wird durch Reaktion von Cobalt - mit Lithiumverbindungen hergestellt (EP 0 473 236 A2).It is known to produce cathodes for molten carbonate fuel cells from lithium cobaltite (LiCo O 2 ). To produce such cathodes, lithium cobaltite powder is mixed with a binder. A dispersant can be added to the binder. A film is formed from the mixture, which is divided into plates. The plates are sintered in an air-carbon dioxide atmosphere at high temperatures. Lithium cobaltite is produced by reacting cobalt with lithium compounds (EP 0 473 236 A2).
Weiterhin ist es bekannt, Lithiumkobaltit durch Reaktion von Cobaltoxid (Eisenoxid) mit Lithiumhydroxiddampf in einer Hochtemperaturreaktion als Pulver herzustellen. Dieses Pulver wird mittels keramischer Sinterverfahren zu bruchempfindlichen Elektrodenplatten geringer Größe verarbeitet (JP 0636, 770).It is also known to produce lithium cobaltite as a powder by reacting cobalt oxide (iron oxide) with lithium hydroxide vapor in a high-temperature reaction. This powder is processed by means of ceramic sintering processes into small-size, fragile electrode plates (JP 0636, 770).
Schließlich ist es bekannt, aus einer duktilen Cobaltschicht, deren Poren mit Lithiumcarbonat gefüllt sind, durch Oxidation eine Lithiumcobaltitschicht zu bilden. Die Umsetzung zur Lithiumcobaltit-Schicht geschieht vorzugsweise nach der Vereinigung mit einer Matrix-Schicht und einer Anoden-Schicht und nach der Einsetzung zusammen mit Stromkollektoφlatten in einen Zellenhalter einer Brennstoffzelle während einer Anfahrphase der Brennstoffzelle. Die Struktur der so hergestellten Lithiumcobaltit- Elektrodenplatte entspricht der Struktur der ursprünglichen porösen Cobaltelektrodenplatte, die einen relativ großen Polarisationswiderstand aufweist (DE 43 03 136 Cl ).Finally, it is known to form a lithium cobaltite layer by oxidation from a ductile cobalt layer whose pores are filled with lithium carbonate. The conversion to the lithium cobaltite layer preferably takes place after combination with a matrix layer and an anode layer and after insertion together with current collectors in a cell holder of a fuel cell during a start-up phase of the fuel cell. The structure of the lithium cobaltite electrode plate thus produced corresponds to the structure of the original porous cobalt electrode plate, which has a relatively large polarization resistance (DE 43 03 136 Cl).
Der Erfindung liegt das Problem zugrunde, ein Verfahren zur Herstellung einer porösen Lithiumcobaltit-Elektrodenplatte mit großer innerer Oberfläche und geringem Polarisationswiderstand anzugeben und eine nach dem Verfahren hergestellte Elektrodenplatte bereitzustellen.The invention is based on the problem of a method for producing a porous lithium cobaltite electrode plate with a large inner surface and a small one Specify polarization resistance and provide an electrode plate produced by the method.
Das Problem wird für das Verfahren erfindungsgemäß dadurch gelöst, daß Cobaltmetall- und Lithiumkarbonatpulver homogen miteinander vermischt werden, daß danach aus der Mischung Folien und aus den Folien Platten erzeugt werden, die zu porösen Elektrodenvorläuferplatten gesintert werden, und daß anschließend die Elektrodenvorläuferplatten bei einer Temperatur zwischen 400°C und 488°C strömender Luft für mehrere Stunden ausgesetzt werden, bis die Elektrodenvorläuferplatten in Lithiumcobaltit-Elektrodenplatten mit extrem großer innerer Oberfläche umgewandelt sind. Bei dem erfindungsgemäßen Verfahren läuft eine strukturbestimmende Bildungsreaktion von Lithiumkobaltit in mehreren Stufen ab. Zunächst findet in der porösen Cobalt/Lithiumkarbonat-Vorläuferelektrodenplatte in der Luftatmosphäre eine Oxidation von Cobalt statt. Weiterhin wird an den Kontaktstellen von Cobaltoxid mit Lithiumkarbonat Lithiumkobaltit und Lithiumoxid unter Abgabe von Kohlendioxid gebildet, das mit der strömenden Luft abgeführt wird. Lithiumoxid geht wegen seines hohen Dampfdrucks in die Gasphase über, in der es an nicht mit Lithiumkarbonat kontaktiertem Cobaltoxid zu Lithiumcobaltit abreagiert.The problem is solved for the process according to the invention in that cobalt metal and lithium carbonate powders are homogeneously mixed with one another, in that the mixture is then used to produce foils and sheets from the foils, which are sintered to form porous electrode precursor plates, and that the electrode precursor plates are then at a temperature between 400 ° C and 488 ° C flowing air for several hours until the electrode precursor plates are converted into lithium cobaltite electrode plates with an extremely large inner surface. In the method according to the invention, a structure-determining formation reaction of lithium cobaltite takes place in several stages. First of all, cobalt / lithium carbonate precursor electrode plate oxidizes cobalt in the air atmosphere. Furthermore, at the contact points of cobalt oxide with lithium carbonate, lithium cobaltite and lithium oxide are formed with the emission of carbon dioxide, which is removed with the flowing air. Because of its high vapor pressure, lithium oxide changes into the gas phase, in which it reacts to cobalt oxide not contacted with lithium carbonate to form lithium cobaltite.
Vorzugsweise wird die Temperatur während der Bildung von Lithiumkobaltit zwischen 420°C und 480°C gehalten. Es hat sich gezeigt, daß in diesem Temperaturbereich die oben beschriebenen Reaktionen unter Einwirkung des Luftsauerstoffs unter günstigen Bedingungen ablaufen.Preferably, the temperature is maintained between 420 ° C and 480 ° C during the formation of lithium cobaltite. It has been shown that in this temperature range the reactions described above take place under the action of atmospheric oxygen under favorable conditions.
Insbesondere wird die Menge der zugefuhrten Luft und die Strömungsgeschwindigkeit der Luft so eingestellt, daß der Kohlendioxidgehalt der Luft nicht größer als etwa 1 % ist und die Dauer der Einwirkung der Luft etwa 10 Stunden dauert. Unter diesen Bedingungen wird eine aus Lithiumcobalit bestehende Elektrode mit sehr großer innerer Oberfläche vonIn particular, the amount of air supplied and the flow rate of the air are adjusted so that the carbon dioxide content of the air is not more than about 1% and the duration of exposure to the air is about 10 hours. Under these conditions, an electrode made of lithium cobalt with a very large inner surface of
2 bis 6m2 / erhalten, die kein Lithiumkarbonat mehr aufweist. /g2 to 6m 2 / obtained, which no longer has lithium carbonate. /G
Die Reaktionen, die bei dem oben beschriebenen Verfahren während der verschiedenen Verfahrensphasen ablaufen, sind nachstehend detailliert angegeben:The reactions that take place during the various stages of the process described above are detailed below:
Mechanismus der Festkörper - Gas - Reaktion (400°C - 488°C)Mechanism of the solid-gas reaction (400 ° C - 488 ° C)
Oxidation von Cobalt:Oxidation of cobalt:
2 12 1
Co + - O2 → - Co3O4 Co + - O 2 → - Co 3 O 4
3 3 Festkörperreaktion an den Kontaktstellen Cobaltoxid / Lithiumkarbonat:3 3 Solid state reaction at the contact points cobalt oxide / lithium carbonate:
- Co3O4 + Li2CO3 + — O2 → LiCoO2 + CO2 + - Li2 O(fest) - Co 3 O 4 + Li 2 CO 3 + - O 2 → LiCoO 2 + CO 2 + - Li 2 O (solid)
LJ2θ(fesl) -> Li2O(gaS) LJ 2 θ (fesl) -> Li 2 O (gaS)
Gasdiffusion von Li2O(gas): Gas diffusion of Li 2 O (gas) :
Li20(gas) (Reaktionsortl) → Diffusion → Li20(gas) (Reaktionsort2)Li 2 0 (gas) (reaction site) → diffusion → Li 2 0 (gas) (reaction site 2 )
Gas - Fest - Reaktion am Reaktionsort 2:Gas - solid - reaction at reaction site 2:
a) - Co3O4 + Li2O(gas) + — O2 → LiCoO2 a) - Co 3 O 4 + Li 2 O (gas) + - O 2 → LiCoO 2
Bei einem nur geringen Kohlendioxidanteil in der Luft, der einen Wert von 1 % nicht übersteigt, erhält man eine aus Lithiumcobalit bestehende Elektrode mit sehr großer innererWith only a small amount of carbon dioxide in the air, which does not exceed a value of 1%, an electrode made of lithium cobalt with a very large inner surface is obtained
Oberfläche von 2 - 6m2 / , die nach 10 Stunden kein Li2CO3 mehr aufweist. Die Struktur, die während dieses kombinierten Oxidations- und Formierprozesses gebildet wird, bleibt bei Einsatz der Elektrode in einer Schmelzkarbonat-Brennstoffzelle erhalten.Surface of 2 - 6m 2 /, which no longer has Li 2 CO 3 after 10 hours. The structure that is formed during this combined oxidation and formation process is retained when the electrode is used in a molten carbonate fuel cell.
Durch Erhöhung des CO2 - Gehaltes in der Luft wird die Li20-Diffusion zu nicht mit Li2CO3 Partikeln kontaktierten, oxidierten Co-Partikeln behindert, da sich aus Li2O und CO2 wieder Li2CO3 bildet. Dadurch verringert sich mit steigendem CO2-Gehalt in der Luft die LiCoO2-Bildungsgeschwindigkeit, und die gewünschte Feinstruktur mit großer innerer Oberfläche kann sich nicht ausbilden.By increasing the CO 2 content in the air, the Li 2 0 diffusion to oxidized Co particles not contacted with Li 2 CO 3 particles is hindered, since Li 2 O and CO 2 again form Li 2 CO 3 . As a result, the rate of LiCoO 2 formation decreases with increasing CO 2 content in the air, and the desired fine structure with a large inner surface cannot form.
Durch Verwendung von befeuchteter Luft mit Wasserdampfgehalten > 2 % kann der Formierprozeß zur Bildung einer großen inneren Oberfläche > 2 m2/g auch mit CO2- Gehalten > 1 % in der Formiergasatmosphäre durchgeführt werden. In diesem Fall erfolgt die Bildung von LiCoO2 durch Reaktion von oxidiertem Cobalt und Lithiumhydroxid nach folgendem Mechanismus.By using humidified air with water vapor contents> 2%, the forming process to form a large inner surface> 2 m 2 / g can also be carried out with CO 2 contents> 1% in the forming gas atmosphere. In this case, LiCoO 2 is formed by the reaction of oxidized cobalt and lithium hydroxide according to the following mechanism.
LiCoO2- Bildung in Gegenwart von Wasserdampf:LiCoO2 formation in the presence of water vapor:
Li2CO3 + H2O(g) → 2LiOH(g) + CO2 Li20(s,g) + H2O(g) → 2LiOH(g) Li 2 CO 3 + H 2 O (g) → 2LiOH (g) + CO 2 Li 2 0 (s, g) + H 2 O (g) → 2LiOH (g)
Diffusiondiffusion
LiOH(g) (Reaktionsort 1) > LιOH(g) (Reaktionsort 2)LiOH (g) (reaction site 1)> LιOH (g) (reaction site 2)
- Co3O4 + LiOH(g) + — O2 → LiCo02 + - H2O(g) - Co 3 O 4 + LiOH (g) + - O 2 → LiCo0 2 + - H 2 O (g)
Eine weitere Erhöhung des Wasserdampfgehaltes über 2 % führt nicht zu einer weiteren Beschleunigung der Reaktion.A further increase in the water vapor content over 2% does not lead to a further acceleration of the reaction.
Das erfindungsgemäße Verfahren kann nach dem Einsetzen der Elektrodenvorläuferplatten in einen Ofen unter den oben beschriebenen Bedingungen durchgeführt werden, wobei die hergestellten Lithiumcobaltit-Elektroden nach dem Abkühlen dem Ofen entnommen und danach mit einer mit dem Schmelzelektrolyten getränkten Matrix- Schicht und einer Anode sowie mit Stromkollektoren zu einer Brennstoffzelle zusammengefügt werden.The method according to the invention can be carried out after inserting the electrode precursor plates into an oven under the conditions described above, the lithium cobaltite electrodes produced being removed from the oven after cooling and then with a matrix layer impregnated with the melt electrolyte and an anode and with current collectors be put together in a fuel cell.
Günstig ist es auch, wenn die jeweilige Elektrodenvorläuferplatte mit einer mit Schmelzkarbonat gefüllten Matrix-Schicht zu einer der Brennstoffzelle entsprechenden Schichtanordnung vereinigt wird und danach mit dieser in eine Brennstoffzelle eingebaut wird, wobei das erfindungsgemäße Verfahren nach dem Einbau in der Brennstoffzelle durchgeführt wird. Unter den Bedingungen des erfindungsgemäßen Verfahrens entsteht dabei während einer Anfahrprozedur der Brennstoffzelle die Lithiumcobaltitkathode. Das Lithiumcobaltit kann auch als dünne, festhaftende Schicht auf einer porösen Unterlage aus Nickel, das dabei oxidiert wird, erzeugt werden.It is also advantageous if the respective electrode precursor plate is combined with a matrix layer filled with molten carbonate to form a layer arrangement corresponding to the fuel cell and is then installed with the latter in a fuel cell, the method according to the invention being carried out after installation in the fuel cell. Under the conditions of the method according to the invention, the lithium cobaltite cathode is formed during a startup procedure of the fuel cell. The lithium cobaltite can also be produced as a thin, firmly adhering layer on a porous base made of nickel, which is thereby oxidized.
Das nachstehende Beispiel dient der weiteren Erläuterung der Erfindung.The following example serves to further explain the invention.
AusführungsbeispielEmbodiment
Als Ausgangskomponenten werden feines Cobalt-Pulver, das in einer Korngröße < 3μm und Li2CO3 - Pulver, das eine Korngöße zwischen lμm und lOμm hat, in einem Verhältnis von 66gew.%Co und 34gew.% Li2CO3 unter Zugabe eines in einem nichtwässrigen Lösungsmittel gelösten organischen Bindemittels, eines Weichmachers, und anderer organischer Zusätze zu einem dickflüssigen Schlicker verarbeitet, der nach dem "Tape casting"-Verfahren zu einer Folie ausgezogen wird. Aus der Folie werden nach dem Trocknungsprozeß Platten hergestellt, die im Schutzgasofen bei einer Temperatur unterhalb des Li2CO3 - Schmelzpunktes, vorzugsweise bei 650°C, 30 Minuten in reduzierender Atmosphäre gesintert werden. Nach dieser Prozedur besteht ein enger Kontakt zwischen den Co- und den Li2CO3 - Körnern in den Elektrodenvorläuferplatten. Nach der Sinterung der Platten wird mit einer Rate von 200 Kelvin je Stunde auf 460°C abgekühlt und nach ausreichender Spülung mit Stickstoff auf Luftatmosphäre mit Luftaustausch gewechselt. Bei dieser Temperatur erfolgt innerhalb von 10 Stunden die vollständige Oxidation von Co unter gleichzeitiger Bildung von Lithiumcobaltit aus dem gebildeten Cobalt-Oxid und Li2CO3 in einer Festkörper- und Gasreaktion. Die so hergestellte Lithiumcobaltit Elektrode hat je nach Bildungsgeschwindigkeit eine extrem große innere Oberfläche, die nach dem Einbau in eine Schmelzkarbonat-Brennstoffzelle und deren Betrieb erhalten bleibt. Die Formiergeschwindigkeit wird bestimmt durch (i) den Gehalt an Kohlendioxid und Wasserdampf und (ii) die Korngröße des Cobalt und des Li2CO3-Pulvers.The starting components are fine cobalt powder with a grain size of <3μm and Li 2 CO 3 powder, which has a grain size between lμm and lOμm, in a ratio of 66% by weight Co and 34% by weight Li 2 CO 3 with the addition of a processed in a non-aqueous solvent organic binder, a plasticizer, and other organic additives to form a viscous slip, which is pulled out into a film using the "tape casting" process. After the drying process, sheets are produced from the film, which are sintered in a protective gas furnace at a temperature below the Li 2 CO 3 melting point, preferably at 650 ° C., for 30 minutes in a reducing atmosphere. After this procedure there is a close one Contact between the Co and the Li 2 CO 3 grains in the electrode precursor plates. After the plates have been sintered, they are cooled to 460 ° C. at a rate of 200 Kelvin per hour and, after adequate purging with nitrogen, they are changed to an air atmosphere with an air exchange. At this temperature, the complete oxidation of Co takes place within 10 hours with simultaneous formation of lithium cobaltite from the cobalt oxide formed and Li 2 CO 3 in a solid-state and gas reaction. Depending on the rate of formation, the lithium cobaltite electrode thus produced has an extremely large inner surface, which is retained after installation in a molten carbonate fuel cell and its operation. The forming speed is determined by (i) the content of carbon dioxide and water vapor and (ii) the grain size of the cobalt and the Li 2 CO 3 powder.
Eine nach dem erfindungsgemäßen Verfahren hergestellte Elektrode hat eine für das Verfahren typische Struktur mit extrem großer innerer Oberfläche. Hierauf beruht ein sehr geringer Polarisierungswiderstand einer entsprechenden Kathode in einer Brennstoffzelle, wodurch deren Leistungsfähigkeit gesteigert wird. An electrode produced by the method according to the invention has a structure typical of the method with an extremely large inner surface. This results in a very low polarization resistance of a corresponding cathode in a fuel cell, which increases its performance.

Claims

P A T E N T A N S P R Ü C H E PATENT CLAIMS
1. Verfahren zur Herstellung einer Elektrode für eine Schmelzkarbonat-Brennstoffzelle, dadurch gekennzeichnet, daß Cobaltmetall- und Lithiumkarbonatpulver miteinander vermischt werden, daß danach aus der Mischung Folien und aus den Folien Platten erzeugt werden, die zu Elektrodenvorläuferplatten gesintert werden, und daß anschließend die Elektrodenvorläufeφlatten bei einer Temperatur zwischen 400°C und 488°C strömender Luft ausgesetzt werden, bis die Elektrodenvorläuferplatten durch Cobaltoxidation und Lithiumcobaltitbildung in Lithiumcobaltit-Elektrodenplatten mit extrem großer innerer Oberfläche umgewandelt sind.1. A method for producing an electrode for a molten carbonate fuel cell, characterized in that cobalt metal and lithium carbonate powder are mixed with one another, that thereafter films are produced from the mixture and from the films plates which are sintered to form electrode precursor plates, and that subsequently the electrode leads φ plates exposed to flowing air at a temperature between 400 ° C and 488 ° C until the electrode precursor plates are converted into lithium cobaltite electrode plates with an extremely large inner surface by cobalt oxidation and lithium cobaltite formation.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Temperatur zwischen 420°C und 480°C liegt.2. The method according to claim 1, characterized in that the temperature is between 420 ° C and 480 ° C.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß der Kohlendioxidgehalt der Luft kleiner als ein Prozent ist.3. The method according to claim 1 or 2, characterized in that the carbon dioxide content of the air is less than one percent.
4. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß der Kohlendioxidgehalt der Luft größer 1 % ist und die Luft einen Wasserdampfgehalt größer 2 % hat.4. The method according to claim 1 or 2, characterized in that the carbon dioxide content of the air is greater than 1% and the air has a water vapor content greater than 2%.
5. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche 1 bis 4, dadurch gekennzeichnet, daß die Elektrodenvorläuferplatten als dünne Schichten auf einer porösen Unterlage aus Nickel abgeschieden werden und daß die Lithiumkobaltit- Elektroden als festhaftende Schichten auf der Nickeloxid-Unterlage erzeugt werden.5. The method according to one or more of the preceding claims 1 to 4, characterized in that the electrode precursor plates are deposited as thin layers on a porous base made of nickel and that the lithium cobaltite electrodes are produced as adherent layers on the nickel oxide base.
6. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Elektrodenvorläufeφlatten in einem Ofen der Cobaltoxidation und Lithiumcobaltitbildung ausgesetzt werden, und daß die Lithiumcobaltit-Elektrodenplatten jeweils nach der Abkühlung mit einer mit Schmelzkarbonat gefüllten Matrix-Schicht und einer Anoden-Schicht zu einer der Brennstoffzelle entsprechenden Schichtanordnung vereinigt werden.6. The method according to one or more of the preceding claims, characterized in that the electrode leads are exposed to cobalt oxidation and lithium cobaltite formation in an oven, and in that the lithium cobaltite electrode plates are each cooled after cooling with a matrix layer filled with molten carbonate and an anode layer can be combined to form a layer arrangement corresponding to the fuel cell.
7. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche 1 bis 4, dadurch gekennzeichnet, daß die Elektrodenvorläuferplatten jeweils mit einer mit Schmelzkarbonat gefüllten Matrix-Schicht und einer Anoden-Schicht zu einer Schichtanordnung vereinigt werden, die in einer Brennstoffzelle angeordnet wird, und daß die Lithiumcobaltit-Kathodenplatte in einer Anfahφhase unterhalb der Schmelztemperatur des LiKC03-Schmelzelektrolyten in der Brennstoffzelle erzeugt wird. 7. The method according to one or more of the preceding claims 1 to 4, characterized in that the electrode precursor plates each with a matrix layer filled with molten carbonate and an anode layer to one Layer arrangement are combined, which is arranged in a fuel cell, and that the lithium cobaltite cathode plate is generated in a start-up phase below the melting temperature of the LiKC0 3 melt electrolyte in the fuel cell.
EP97904358A 1996-02-03 1997-01-31 Process for the production of an electrode for a fused carbonate fuel cell, electrode produced according to this process and fused carbonate fuel cell provided with an electrode produced according to this process Expired - Lifetime EP0878028B1 (en)

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DE19603918A DE19603918C2 (en) 1996-02-03 1996-02-03 Process for producing an electrode for a molten carbonate fuel cell and its use
DE19603918 1996-02-03
PCT/EP1997/000422 WO1997028571A1 (en) 1996-02-03 1997-01-31 Process for the production of an electrode for a fused carbonate fuel cell, electrode produced according to this process and fused carbonate fuel cell provided with an electrode produced according to this process

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DE19721546C1 (en) * 1997-05-23 1998-10-22 Mtu Friedrichshafen Gmbh Double layer cathode for molten carbonate fuel cell
EP2390307A1 (en) 2010-05-27 2011-11-30 Corning Incorporated Porous ceramic processing using prilled wax and non-ionic surfactant

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US3607417A (en) * 1967-12-04 1971-09-21 Ionics Battery cell
JPS60117566A (en) 1983-11-29 1985-06-25 Matsushita Electric Ind Co Ltd Molten carbonate fuel cell
NL9001916A (en) * 1990-08-30 1992-03-16 Stichting Energie TAPE SUITABLE FOR USE IN FUEL CELLS, ELECTRODE SUITABLE FOR USE IN A FUEL CELL, METHOD FOR SINTERING SUCH ELECTRODE AND FUEL CELL FITTED WITH SUCH ELECTRODE.
DE4303136C1 (en) * 1993-02-04 1994-06-16 Mtu Friedrichshafen Gmbh Molten carbonate fuel cell - comprises matrix layer impregnated with molten electrolyte contg. lithium carbonate, having anode and cathode layers on either side
IT1269173B (en) * 1994-01-04 1997-03-21 Finmeccanica Spa METHOD FOR THE MANUFACTURE OF FUEL CELL CATHODES
IT1269334B (en) * 1994-04-19 1997-03-26 Finmeccanica Spa Azienda Ansal METHOD FOR THE MANUFACTURE OF FUEL CELL CATHODES
WO1996008050A1 (en) 1994-09-09 1996-03-14 Stichting Energieonderzoek Centrum Nederland Double tape suitable for use in molten carbonate fuel cells
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DE19603918A1 (en) 1997-08-07
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US6238619B1 (en) 2001-05-29
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